The present invention relates to the methods for the preparation of nanosized material particles. (xe2x80x9cNano-materialsxe2x80x9d in connection with the present invention comprise transition metals and alloys; metal oxides; and ceramic compositions having a small nanosize, i.e. about 1-6 nm.) Nanomaterials are prepared from the corresponding precursors i.e. the corresponding metal salts or alkoxides by suitable chemical reactions, e.g. reduction, hydrolysis and exchange processes under mild conditions.
There are known methods to prepare clusters or fine colloids from said nanomaterials which are dispersed in different suitable solutions. Appropriate liquid media enable the production of different preparations, which may be used as thin films on various supports.
There are known several methods for the preparation of ultrathin films of metal particles on solid supports, e.g. ion implantation (M. Che. C.O. Bennet, Adv. Catal. 1989, 36, 55); organometallic chemical vapor deposition (A. Sherman, Chemical vapor Deposition for Microelectronics, Principles, Technology and Application. Noyes Publications; Park Ridge, N.J. 1987; and N. E. Dryden et. al., Chem. Mater. 1991, 3, 677); metal deposition from colloidal solution (G. Schmid, Chem. Rev. 1992, 92, 1709); reductive metal deposition from aqueous salt solution (I. Coulthard, et. al., Langmuir 1993, 9, 3441.): photodecomposition of metal complexes in thin films (R. Krasnasky et. al. Langmuir, 1991, 7, 2881); and photo-reductive deposition from Pd(II) complexes in solution (K. Kondo et. al., Chem. Lett. 1992, 999) Other technics are based on the film formation of noble metal loaded block copolymers (Y. NgCheongChan et. al., Chem. Mater. 1992, 4, 24; and J. P. Spatz, et al., Adv. Mater. 1995, 7, 731.); on the Langmuir-Blodget (LB) transfer of monolayers or surfactant stabilized metal colloids (F. S. Meldrum et. al., Langmuir 1994, 10. 2035; and F. S. Meldrum. et al., Chem. Mater. 1995. 7, 1112); and on thermal decomposition of LB films of zero valent palladium complexes (E. Maasen et. al., Langmuir 1996, 12, 5601).
At present the microelectronic and some related industries, mainly continue to use the vapor deposition method. The xe2x80x9cWetxe2x80x9d method, which is a method of film deposition from solutions, provides a good challenge for the industry since it does not require high temperatures and pressures or high vacuum and enables to vary the properties of the nano compositions to a large extent
During the last decade, the number of scientific works devoted to the synthesis of nanomaterials in solutions has significantly increased. Certain practical results were reported. Thus, for example G. Schmid (see above) demonstrated that the pellets which consist of ligand stabilized golden clusters (derived from a liquid) may be regarded as tunneling resonance resistors and, additionally, as cellular automates. The density of electronic switches, compared with common semiconductors increased in another example to a factor of 105-106. Another paper (T. Yamamoto, in Macromolecular Complexes, Ed. by Eishun Tsuchida, VCH, 1993, 380-395.) informed about the preparation of electrically conducting polymer compositions by using organosols of metal sulfides. The polymer-composite films not only show good electrical conductivity but were also controlled to p- or n-type conductors.
The realization of quantum dots, of uniform size and structure opens the door to multiple switches. This enables the manufacture of new generations of computers with extremely high capacities. The manufacture of novel mini-lasers, based on quantisizing particles, will most probably lead to optoelectronic switches, operated simultaneously by photons and electrons. Nanometal coatings may be effectively used, e.g as film catalysts (for instance in the processes of electroless metal deposition); and as modifiers of mechanical properties of different materials.
However, all said conventional methods are not satisfactory in the preparation of coatings comprising nanomaterial particles, as they are rather complicated, expensive or do not yield the particles having the desired size.
It has thus been desirable to find a method which would overcome said disadvantages, i.e should not be complicated, not be too expensive and yield nanomaterial particles having the desired size.
It is well known that water which appears to be a key factor which governs the association of surfactants in different solvents, functions not only as an inert solvent but plays a significant part in the mechanism of chemical processes. (Garti et. al. Coll. and Interface Sci. 178 (1996) p. 60-68). When describing the state of water in relation to any surface a distinction is usually made between xe2x80x9cbulkxe2x80x9d and xe2x80x9cboundxe2x80x9d water. It is assumed that xe2x80x9cbulkxe2x80x9d or free water has physico-chemical properties which are not very different from those of pure water. xe2x80x9cBoundxe2x80x9d water may be defined by the operational definitions which refer to the water detected by a certain technique.
According to the method utilized by Senatra (D. Senatra et. al. Can. J. of Phys. 68 (1990) p. 1041), in which the endothermic scaling made was applied and the peaks representing various states of water were identified and analyzed, it was shown that xe2x80x9cfreexe2x80x9d water melts at 0xc2x0 C., xe2x80x9cinterfacial boundxe2x80x9d water melts at xe2x88x9210xc2x0 C., and non-freezing water which is the most strongly bound part of bound water has no peaks on thermograms up to xe2x88x92100xc2x0 C.
It has been found that the state of the water in water-organic-surfactant organized solutions is strictly correlated with the size of the particles. Particles which have a diameter of less than 5 nm are synthesized in systems which comprise only strongly bound water (non freezing water according to subzero differential scanning Calorimetry DSC).
In developing the method according to the present invention it has been considered:
a. producing the water-organic-surfactant organized solutions (complex liquids) comprising nanosized particles in particular having a diameter of 1-5 nm which are useful for the particle preparation;
b. regulating the water content in such a manner that the whole water will be strongly bound to the surfactant (non-freezing) in the system, thus enabling to provide nano particles which have a diameter of less than 5 nm;
c. the regulation of the solution structures which enables the regulation of the morphology of the particles;
d. the variation of the chemical composition and concentration of nano-precursors (and of the complementary reactants), which enables the control of the particle size distributions (PSD) and of the thickness of the protecting shells;
e. using different polymers which enable the production of films having different adhesion properties, by the deep coating method; and
f. the control of the viscosity and of the velocity of the solutions which lead to different film thicknesses;
The optimization of the above-mentioned factors (which should operate simultaneously) should lead to the production of the coating having the desired properties.
The present invention thus consists in a method for the production of nanomaterial particles (as herein defined) in which:
said nanomaterial particles are synthesized in the solutions of complex liquids containing non-freezing water from suitable precursors, which precursors are selected from suitable surfactants, metal salts and alkoxides by a suitable chemical reaction under mild conditions; and
preparing from said materials fine colloids dispersed in various polymer solutions.
The nanomaterial particles have advantageously a diameter of 1-5 nm.
The water in the solution is advantageously non-freezing water as determined by low temperature different scanning calorimetry
The suitable chemical reaction may be selected, for example, among reduction, hydrolysis and exchange processes.
Mild conditions in connection with the present invention are suitably atmospheric pressure and a temperature range of room temperature to 70xc2x0 C.
Suitable solutions may be selected among suitable water-organic-surfactant solutions; (microemulsions; liquid crystalline media; etc.)
Suitable organic solvents may be, e.g. selected among suitable hydrocarbons (octane, decane, dodecane); chlorinated hydrocarbons (1,2-dichloroethane); ethers (ethylether); etc.
The appropriate liquid media enable the preparation of different self assemblies of nanomaterials and subsequently the use of them as thin films on various supports.
Suitable surfactants are, for example,:
Quaternary ammonium salts, e.g. trioctylmethyl ammonium chloride (Aliquat 336), dioctyldimethylammonium bromide (DDAB), cetyltrimethylamnonium chloride (CTAB), etc,; sodium bis-(2-ethyl-hexyl)-sulfosuccinate; poly-ethoxyethylene-10-oleyl ether (Brij 96; etc. Metal oxide precursors may be, e.g. alkoxides:
tetraethoxy silane (TEOS); tetramethoxy silane (TMOS); Al, Zr isopropoxides, etc.;
Fe, Mg and Al chlorides; Al and Mg acetates; Na and K orthosilicates; Zr oxychloride; etc. Metal precursors may be, e.g. transition metal salts of Fe, Co, Ni, Cu, Ru, Rh, Pd, Ir and Pt, e.g. FeCl3, K2PDCl4, K2PtCl4 and CuCl2.
The polymers may be selected, e.g. from polyethylene oxide (PEO), polyvinyl chloride (PVC), polyvinyl alcohol (PVA), polymethyl methacrylate (PMMA), etc.
Suitable reducing agents are, for example, sodium formate; hydrogen; certain alcohols (methanol, ethanol, isopropylalcohol); etc.
The method according to the present invention can direct the morphology, dimension and homogeneity of the size distributions of the small colloids (and clusters) and also their self assembling.